Development of engine noise reduction technologies can reduce engine noise in vehicles such as automobiles. On the other hand, road noise due to oscillation input from the road has been becoming more perceivable during travel of a vehicle. A suggested cause of the road noise is acoustic cavity noise that occurs in a tire-internal space which is sealed by a tire and a rim portion of a vehicle wheel. The acoustic cavity noise is produced since the oscillation input from a road during travel of the vehicle causes a standing wave at a wavelength of the circumference of the tire-internal space and the standing wave causes air column resonance at a particular frequency (180 to 270 Hz).
As methods for reducing the acoustic cavity noise, configurations have been known where Helmholtz resonant sound absorber, Quincke interference silencer, and sound absorbers using side branch resonance are applied. A configuration where a plurality of auxiliary air chambers are formed circumferentially in a rim portion of a vehicle wheel and holes that communicate the auxiliary air chamber with the tire-internal space are provided is proposed in JP-A-2003-326904 (“JP ‘904’”), for example. Such a configuration is equipped with the Helmholtz resonant sound absorber formed with the auxiliary air chambers and is capable of reducing the acoustic cavity noise that occurs in the tire-internal space. A method that a vertical wall protruding outward in the radial direction from an outside surface of the rim portion is molded along the circumferential direction, a plurality of partition walls in the front-back direction are molded along the circumferential direction, the vertical wall is bent, and the bent vertical wall and the partition walls thereby form the plurality of auxiliary air chambers is also proposed in “JP ‘904’”.